[Fix] Ignore extensions label should only show each extension once #1070 (#1080)

* Removed repeated extensions on the ignore extensions label

* Fix linter

Co-authored-by: bsande6 <bsande6@g.clemson.eu>
Co-authored-by: Frédéric Collonval <fcollonval@users.noreply.github.com>

Author: 3 people

src/commandsAndMenu.tsx

@@ -1039,7 +1039,8 @@ export function addCommands(
       const { files } = args as any as CommandArguments.IGitContextAction;
       const extensions = files
         .map(file => PathExt.extname(file.to))
-        .filter(extension => extension.length > 0);
+        .filter(extension => extension.length > 0)
+        .filter((item, index, arr) => arr.indexOf(item) === index);
       return trans._n(
         'Ignore %2 extension (add to .gitignore)',
         'Ignore %2 extensions (add to .gitignore)',